Rectification I selected "the newly created EFI System Partition" to install the bootloader, but in reallity it installed the bootloader on the Windows 8 EFS...
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KourosDec 28 '12 at 17:07

Did you do a backup beforehand? i.e the windows 8 start/system partition is something small like 150-350 MB so maybe you did dd if=/dev/sda1 of=/media/some_usb_pendrive/backupfile? If such a backup exists I would restore the windows system/start partitio which might have been "damaged".
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humanityANDpeaceDec 28 '12 at 17:58

Sorry no backup but I managed to get Windows 8 back using Recovery Environment (by pressing the assist button instead of the power on button)
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KourosJan 4 '13 at 10:39

Add a custom entry to GRUB bootmenu

You can use Ctrl+Alt+T to open a terminal and run sudo nano /etc/grub.d/40_custom, then copy and paste the code. Finally then press Ctrl+O to save and Ctrl+X to leave.

Heads up:hd0,gpt1 here is the ID of my EFI System Partition (ESP). If your ESP is not the first partition on your first harddrive during boot, then yours is different! E.g. hd1,gpt2 for the second partition on the second drive.

Replace part_gpt with part_msdos if the drive uses MBR and legacy partitioning and also change hd0,gpt1 to hd0,msdos1 respectively.

Apply changes to GRUB

Simply run the following command, which should generate a new GRUB configuration, including the new custom entry:

what should i 'aim' for? i thought it was the windows data partition (gpt4 here) but it worked with gpt1, which is the only EFI partition i have. i though installing ubuntu would have overwritten the windows content of the EFI partition, like grub does to the MBR...
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gcbFeb 15 '13 at 6:16

1

This solution is not working for me. Is the character ` appearing in the set root='(hd0,gpt1)' intended. It gives error for me (I try with gpt3) even without that character also. The error is like (hd0,gpt1) is not found.
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iammilindAug 2 '13 at 12:12

I had to disable "secure boot" in the bios before this would work.
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Robin WinslowApr 30 '13 at 16:21

@RobinWinslow Yes, Boot-Repair also worked for me (Lenovo Thinkpad S540) but only if I disabled SecureBootin the bios, otherwise Windows 8 still complains...Would be nice if this could be made to work whilst retaining SecureBoot
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fpghostDec 19 '13 at 10:04

Under W8, in an elevated privilege command window, run powercfg /h off. By the time you do this, W8 may already have overwritten the EFI partition. It took me a few iterations of changing bootmgfw.efi and having it reset until it stuck, but now I'm happy.

I can't tell if just booting W8 is enough, or if you have to log in and then reboot. Perhaps somebody with more patience (I was working on this for more than half a day) can tell.

I have the same problem on my Asus-x202 laptop (running W8 & Ubuntu 13.04).

A slightly annoying work around is good enough for me for the moment: in the boot menu go to system (or start bios from the start using probably f2). If you use the override to boot, Windows will start as usual.

@edwin This answer could use expanding, but it does appear to be an attempt to answer the question that was asked. vic: Welcome to Ask Ubuntu! I recommend editing this to add more information about how to use that feature, as well as a more thorough explanation of why it solves this problem. Thanks.
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Eliah KaganAug 16 '13 at 0:58

I have a similar issue with my new HP Pavillion Sleekbook, Model 15-b142dx. It came with W8 pre-loaded. I was able to re-size the Windows partition from within Windows, then installed 64-bit Ubuntu 13.04 from a thumb drive. However, on reboot, W8 started normally, with no boot menu. So, I used "boot-repair", which made the system unbootable. On start-up, it would print:

Failed to open \EFI\Microsoft\Boot\grubx64.efi - 800000000000000E
Failed to load grub
Failed to open \EFI\BOOT\grubx64.efi - 800000000000000E
Failed to load grub
Failed to open \EFI\BOOT\grubx64.efi - 800000000000000E
Failed to load grub

It would then shut down.

After some trial and error, I found that pressing F10 during boot would take me to the BIOS, where I could disable Secure Boot. The next boot, I got a LONG menu from grub, with lots of entries like:

These were all contained in a file, "/etc/grub.d/25_custom". I made a backup copy of that file, then eliminated all the entries except Windows Boot UEFI loader. (This is one of the entries that allows W8 to boot). I then ran "update-grub", and wound up with a much nicer boot menu, and can boot either OS.